Fine-Tuning Fertility Programs Pays Dividends, Experts Say

By Alexander Litvin

For farmers, marginalized economic yields are aggravated by increasing costs of fertilizer, labor and capital machinery reducing profitability. Nutrient loss from inefficient fertilizer application and runoff further complicates production economics and our ecosystem's balance.

To provide technical assistance and improve productivity and profitability of farmers, the Iowa Soybean Association (ISA) hosted the annual 4R Nutrient Stewardship Event at the Iowa State University (ISU) Alumni Center in Ames.

By managing a fertility program with emphasis on the right source, the right rate, the right time, and the right place, farmers can increase production, profitability, and contribute to sustainability. These four Rs refer to best management practices to match fertilizer selection, amount and rate to your crop, while employing strategies to keep those nutrients in the field for maintained returns.

The event was sponsored by ISA, Corteva, Yara, The Fertilizer Institute, Mosaic, Environmental Tillage Systems, Agriculture Clean Water Alliance (ACWA) and 4R Nutrient Stewardship.

Attendees learned from experts on how to build and fine tune their fertility programs through improving their applications and timing of nitrogen (N), phosphorous (P), and potassium (K). Attendees came prepared to discuss their own battles and questions with fertility management, yield economics and sustainable agriculture.

Additional discussions on water sampling and implementation of conservation practices further reinforced the progress Iowa farmers continue to make in increasing sustainable practices while improving the profitability on their farms.  

Building and fine-tuning a fertility program 

Dr. Antonio Mallarino, professor of soil fertility and nutrient management from the Department of Agronomy at ISU reiterated that over-application of P may be hurting farmers’ bottom line more than they realize.

Demonstrating differences between dry and moist soil samples for nutrient analysis, Mallarino displayed how overall yield potential is affected by the amount of P applied. Incremental yield boosts become negligible past a certain rate, but the weight of its cost only skyrockets. With soil nutrient levels categorized as very low, low, optimum, high and very high, he noted that the greatest gain to productivity came from the small increase in P driving nutrient levels from very low to low.  

The timing of application for P and K further provides opportunities for more cost-efficient nutrient management, explained Dr. Daniel Kaiser, associate professor from the Department of Soil, Water and Climate at the University of Minnesota.

Timing matters, as nutrient application significantly affects its efficiency, Kaiser said. Timing of P and K application, starter fertilizer, inhibitors and biologicals can affect productivity and cost. Soil type, crop rotation and time of year should all be considered when deciding when to apply nutrients.

While some exceptions exist, Kaiser noted that in-season application of P and K is not necessarily recommended. In many cases, managing what is already there can be more efficient, and proactive management through soil testing is preferred. Though there is substantial information about biological amendments, he cautioned there were many factors at play in their use, emphasizing the need for careful handling, storage and testing as their effectiveness can vary, so thorough evaluation is crucial.  

Improving nitrogen management and ISA water monitoring and conservation 

A conversation on nitrogen management was led by then ISA Research Agronomist Scott Nelson and Ryan Reimer, precision sales agronomist with E4 Crop Intelligence. Nelson reminded attendees that how and when N is applied can have large implications for yield, just as with P and K. For example, split applications of N can benefit crops in early stages, but that benefit is reduced as the crop progresses beyond the V6 stage. Nelson pointed out that N should be applied per crop needs, splitting between the base rate and later in-season applications.   

Using variable rate nitrogen, as described by Reimer, also offers a way to maintain yields while adjusting fertilizer application and cost in the field. He advocated a methodical strategy for growers looking to optimize their N usage. Beginning with small adjustments, the program first recommends curtailing some N and then increasing gradually while introducing variable rates. Since N is easily impacted by soil temperature and moisture, the efficacy of these changes is validated through meticulous methods, including tissue sampling, scouting, stalk nitrate tests, NDVI Images and yield data. By overlaying data layers and subdividing fields into zones, Reimer explained that in consistently lower-yielding areas of the field, reducing N rate with population, resulted in increased profitability and N efficiency. This is an example of using technology to uniquely manage sections of the field to optimize profitability. 

Understanding water quality is paramount for increasing sustainable farming practices. The ISA Water Lab Service Manager Anthony Seeman discussed the pivotal role of water quality in crop management. Seeman stressed water quality monitoring's importance, from baseline setting to evaluating nutrient strategies and conservation impact.

Seeman pointed to trends in cover crop rotations, with lower nitrate concentrations observed over time, indicating long-term benefits of conservation practices. Water quality is inevitably tied to effective crop management. This shows that crop management, including the implementation of cover crops, can improve sustainability and productivity on the farm.